The present invention relates generally to systems for providing tactile feedback. More specifically, the invention relates to haptic interfaces for providing physical, visual, and auditory feedback to users manipulating objects in a virtual environment.
Virtual reality technologies have expanded in recent years well beyond the entertainment realm of amusement games and fantasy lands to the more commercial fields of product development, testing, and training. One particularly dynamic field of application for virtual reality technologies is the environment of haptic interfaces. Haptics is the field of tactile feedback in which a resistance force is applied in response to and against a user-initiated movement, which thereby imparts a sensation of touch to the user. By programming a computer with the space, surface, and location parameters of a predetermined space and/or object, a user of a haptic interface can simulate or model a sensation of xe2x80x9cfeelingxe2x80x9d a particular object or manipulating the object in space without actually touching the surface or the object itself. Such a system is disclosed in U.S. Pat. No. 5,999,168 to Rosenberg, et al. Another haptic system is described in U.S. Pat. No. 5,802,353 to Avila, et al., one of the inventors of the present invention.
The haptic interface actually includes a broader range of equipment than is typically associated with a computer interface. FIG. 1 shows a typical haptic interface system that includes a computer or processor 100 with memory (not shown) for storing space, location, and resistance data associated with a given object(s) or space. Connected to the computer is a display screen 102 for viewing the manipulated object in virtual space. The user 108 grasps a haptic device 106, which is typically an articulated arm with sensors to detect at least three directions of movement, also known as three degrees of freedom. Therefore, when the user 108 manipulates the object in virtual space by moving the haptic device 106, the sensors detect the combined movement in the three degrees of freedom, communicate the movement to the computer 100, which in turn translates the haptic device movement into actual movement of the object as displayed on the screen 102. Although haptics feedback force cannot presently be experienced merely by viewing the object in virtual space, the virtual effect of the object movement can be viewed by the user 108 on the display screen 102 or, alternatively, through a user headset with goggles 104. As the object is moved in virtual space toward another object or an edge of the virtual space by operation of the haptic device 106, the computer 100 detects when the relative spaces occupied by the objects coincide, thus detecting a collision, and directs the motors in the haptic device 106 to resist further movement by the user 108 in the direction of the collision, thereby providing tactile feedback to the user 108 that the objects are in virtual contact.
Present haptic systems are directed toward product development and testing environments, such as the automotive CAD field disclosed in U.S. Pat. No. 5,694,013 to Stewart, et al., in which an object is manipulated within a virtual space representative of an actual or planned physical environment. However, such systems are limited to determining whether or not a collision has actually occurred between the object and a component within its virtual space. Unfortunately, in the real world, collisions are to be avoided and near-collisions should be learned from, which is not the direction that many of the present haptic interface systems have taken.
Early haptic systems were limited to three degrees of freedom. With more powerful computers, increased memory, and more sophisticated haptic devices, a rotational or torque motion can now be applied within each of the three directions of movement, thereby increasing the degrees of freedom available from the haptic device to six. However, to leap from three to six degrees of freedom is very expensive, not only in the design and commensurate complexity of a six degree of freedom haptic device, but also in the increased number of motors from three to six. A haptic interface system that can provide six degrees of freedom without significantly increasing the equipment cost and complexity would be desirable.
Sophisticated haptic interfaces that accommodate the manipulation of complex polygon objects in a virtual space often rely on continuous polygon versus polygon intersection tests, which constitute an immense computational load on the computer 100. Presently, the standard for haptic interface systems is to test whatever is being moved for collision with a stationary article or environment at one thousand times per second, or at 1,000 Hz. The advantage of maintaining at least the 1,000 Hz standard is a more realistic sensation from the haptic device in the form of a smooth rather than jerky or intermittent resistance to the user""s movements. As the objects being subjected to movement within haptic systems become more complex, the computer 100 must become correspondingly faster and, often, more expensive and physically larger. Despite the huge advances in the capacity of personal computers, the computer processing power required to maintain the 1,000 Hz standard is often beyond the resources of reasonably-priced and configured personal computers. It would be desirable to provide a haptic interface system that could accommodate the virtual manipulation of intricate objects in a complex environment on a personal computer.
The preferred embodiments of the present invention overcome the problems associated with existing haptic interface systems.
The present invention is directed toward a haptic interface for detecting and avoiding collisions between objects in a virtual space in which a user can manipulate one or more objects relative to a fixed object. As the user moves an object that is proximately close to another object, haptic feedback forces provide resistance against the user""s attempted manipulation of the movable object that would result in a contact or collision between the movable object and the stationary other object. One example of the use of such a system would be a modeled disassembly of an aircraft engine in which the user grasps an engine part in virtual space and attempts to remove the component from the engine without colliding with any other portion of the engine. The resistance provided by the present invention not only signals to the user that the part being removed is approaching close proximity with another part of the engine but also indicates, with very high resistance, that the part cannot be removed along the path selected by the user without colliding with some part of the engine. During the virtual manipulation, the user may view the interaction of the objects on a display screen and/or through a head-mounted display.
The present haptic interface relies on a simple intersection comparison to test for an impending or actual collision between objects in the virtual space as opposed to the more complex polygon versus polygon collision test that is typically employed to detect collisions in haptic systems. By establishing a series of points and surface vectors representing each object, the present system can easily and quickly determine impending collisions and actual collisions by analyzing vectored distances between approaching object surfaces.
In an alternate embodiment of the invention, the haptic interface can provide feedback associated with six degrees of freedom without the additional expense and complexity typically associated with expanding from three to six degrees of freedom that add the three rotational torques to the feedback system. Instead of relying on additional motors in the haptic device to provide feedback forces associated with rotational degrees of freedom, the present invention communicates these degrees of freedom to the user in the form of sound and/or visual signals.